Diffusion and Osmosis

The Cell Membrane

TEM picture of a real cell membrane. About Cell Membranes All cells have a cell membrane Functions: Controls what enters and exits the cell to maintain an internal balance called homeostasis Provides protection and support for the cell TEM picture of a real cell membrane. 3

Some molecules are too big to pass through the membrane 4

Passive Transport by proteins Some transport proteins, called channel proteins, form channels that allow specific molecules to flow through.

About Cell Membranes (continued) Structure of cell membrane Lipid Bilayer -2 layers of phospholipids Phosphate head is polar (water loving) Fatty acid tails non-polar (water fearing) Proteins embedded in membrane Phospholipid Lipid Bilayer 6

Where would you be least likely to find water in the cell membrane? Polar heads love water & dissolve. Non-polar tails hide from water. Carbohydrate cell markers Proteins 7

About Cell Membranes (continued) Cell membranes have pores (holes) in it Selectively permeable: Allows some molecules in and keeps other molecules out The structure helps it be selective! Pores 8

A cells contents would be the same as its surroundings without selective permeability

Structure of the Cell Membrane www.teachertube.com/viewVideo.php?video_id=144202&title=Cell_membrane Outside of cell Carbohydrate chains Proteins Lipid Bilayer Transport Protein Phospholipids Inside of cell (cytoplasm) Go to Section: 10

What macromolecule helps move molecules Through channels or pumps What macromolecule helps move molecules Through channels or pumps? Proteins What keeps tails from sticking together? Cholesterol Which macromolecule stick out from the cell And act like ID cards to identify other cells? Carbohydrates

Types of Cellular Transport high low Weeee!!! Passive Transport cell doesn’t use energy Diffusion Facilitated Diffusion Osmosis Active Transport cell does use energy Protein Pumps Endocytosis Exocytosis high low This is gonna be hard work!! 12

Passive Transport (HighLow) cell uses no energy molecules move randomly Molecules spread out from an area of high concentration to an area of low concentration. (HighLow) Three types: 13

3 Types of Passive Transport Diffusion Facilitative Diffusion – diffusion with the help of transport proteins Osmosis – diffusion of water 14

Passive Transport: 1. Diffusion Diffusion: random movement of particles from an area of high concentration to an area of low concentration. (High to Low) Diffusion continues until all molecules are evenly spaced (equilibrium is reached)-Note: molecules will still move around but stay spread out. http://bio.winona.edu/berg/Free.htm 15

Example of Diffusion Diffusion occurs because molecules constantly Smell of cookies baking in the oven Diffusion occurs because molecules constantly move and collide with one another

Passive Transport by proteins Passive transport of materials across the membrane using transport proteins is called facilitated diffusion. Channel proteins Plasma membrane Concentration gradient

Facilitated diffusion (Channel Protein) Diffusion (Lipid Bilayer) Passive Transport: 2. Facilitated Diffusion A B 2. Facilitated diffusion: diffusion of specific particles through transport proteins found in the membrane Transport Proteins are specific – they “select” only certain molecules to cross the membrane Transports larger or charged molecules Facilitated diffusion (Channel Protein) Diffusion (Lipid Bilayer) Carrier Protein 18

Passive Transport: 2. Facilitated Diffusion Glucose molecules Cellular Transport From a- High High Concentration Cell Membrane Low Concentration Protein channel Low Transport Protein Through a  Go to Section: 19

Passive Transport: 3. Osmosis 3.Osmosis: diffusion of water through a selectively permeable membrane Water moves from high to low concentrations Water moves freely through pores. Solute (green) to large to move across. 20

What controls osmosis? Unequal distribution of particles, called a concentratio n gradient, is one factor that controls osmosis. After Osmosis Before Osmosis Selectively permeable membrane Water molecule Sugar molecule

Three solutions

Isotonic Solution Isotonic: The concentration of solutes in the solution is equal to the concentration of solutes inside the cell. Result: Water moves equally in both directions and the cell remains same size! (Equilibrium) 23

Isotonic- water moves in and out of cell in equilibrium

Cells in an isotonic solution water molecules move into and out of the cell at the same rate, and cells retain their normal shape. H2O H2O Water Molecule Dissolved Molecule

Cells in an isotonic solution A plant cell has its normal shape and pressure in an isotonic solution.

Hypotonic Solution Hypotonic: The solution has a lower concentration of solutes and a higher concentration of water than inside the cell. (Low solute; High water) Result: Water moves from the solution to inside the cell): Cell Swells and bursts open (cytolysis)! 27

Hypotonic- water concentration is higher outside of the cell, water enters and cell swells

Cells in a hypotonic solution Plant cells swell beyond their normal size as pressure increases. (plants prefer this –it makes the leaves firm)

Hypertonic Solution Hypertonic: The solution has a higher concentration of solutes and a lower concentration of water than inside the cell. (High solute; Low water) shrinks Result: Water moves from inside the cell into the solution: Cell shrinks (Plasmolysis)! 30

Hypertonic- water concentration is higher in the cell than out- water leaves and the cell shrinks

Cells in a hypertonic solution Plant cells lose pressure as the plasma membrane shrinks away from the cell wall. PLASMOLYSIS

What type of solution am I? H2O H2O Isotonic Hypotonic Hypertonic

B C A What type of solution are these cells in? Hypertonic Isotonic Hypotonic

How Organisms Deal with Osmotic Pressure Bacteria and plants have cell walls that prevent them from over-expanding. In plants the pressure exerted on the cell wall is called turgor pressure. A protist like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from over-expanding. Salt water fish pump salt out of their specialized gills so they do not dehydrate. Animal cells are bathed in blood. Kidneys keep the blood isotonic by remove excess salt and water.